Slashdot videos: Now with more Slashdot!

View

Discuss

Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).

Dr Max writes "Not only is graphene the strongest, thinnest and best conducting material known to man, it is now shown to have superpermeability with respect to water as well. This allows a membrane made with graphene to pass water right through it (PDF), while another atom or molecule (even helium) gets blocked. 'The properties are so unusual that it is hard to imagine that they cannot find some use in the design of filtration, separation or barrier membranes and for selective removal of water,' said one of the researchers."

That's a narrow view of what is in water. Distilled / deionised water is incredibly bad for you. We can't just mix H2O and NaCl, it won't support life. Water needs a long list of nutrients and other molecules like dissolved oxygen before it can support life.

I know its not relevant at the scale we're talking, but I'm just pointing it out, there's no point in adding the salt back by itself.

Even if it does not, I would think it would be much more resilient toward chlorine and iron. Perhaps it won't need as much pretreatment done to the water as a conventional film membrane requires. Currently most decent RO systems have a 10 micron sediment filter, followed by 5 and 1 micron carbon filters. If you have high iron content in the feed water, then you need a softener or some other way to reduce it prior to the sediment filter too. Since the three RO pre-filters typically need to be replaced every 6-12 months, they are the most frequent replacement item. A typical RO membrane last 2-5 years. Perhaps this would be lengthened too.

There has also been studies showing you can make a selective filter by making nanotubes with the right diameter to let water through but not larger molecules. In addition because the walls are so "smooth" there is much less pressure to flow the water through then expected.

I don't really know, but I'd suspect that it has something to do with like,electrical charge or something, not size - e.g. they're both small enough to fit through, but the helium experiences some sort of repulsive force which the water does not as it passes through the field created by the graphene.

This is what they said:"In conclusion, unimpeded evaporation of water through Heleaktight membranes sounds next to impossible. The closest analogy is probably the permeation of protons (atomic hydrogen) through thin films of transition metals, the phenomenon known as superpermeability. To explain our experiments, we propose the model that can be summarized as follows. GO laminates contain 2D capillaries that, under ambient conditions, are filled with an ordered monolayer of water. A capillarylike pressure p

Exactly. Which doubles it's uses not only as a water filter but as a strong light weight container for almost anything. I'm thinking Airships that don't need re-filling and light weight gas tanks for fuel cells.

According to TFA (well, the BBC article on the same subject, anyway) it blocks helium molecules with what appears to be 100% efficiency. Helium molecules are smaller than the molecules in a standing mass of hydrogen, since hydrogen atoms bond together to form H2.

There has also been studies showing you can make a selective filter by making nanotubes with the right diameter to let water through but not larger molecules. In addition because the walls are so "smooth" there is much less pressure to flow the water through then expected.

Although I doubt this orientation will allow for filtering out "helium" as the original posting.

The mechanims that the original posting paper is speculating, it that the way they made the graphene oxide (not pure graphene) membrane, it is has embedded capilaries which when wet (filled with water) allow for nearly unimpeded transport of water, but when these capilaries dry out, their diameter constricts so that nothing gets through (even helium).

So to contrast, the "tubes" are not rigid and the walls are not so "smooth" in this case, the "tubes" are sort of like chinese finger puzzles. When filled with water, allow water to pass easily, but when you try to pull the last bit of water out of them, the diameter constricts and nothing can get past.. Well maybe the chinese finger puzzle analogy was a bad one, but I couldn't think of anything else...

You do, of course. Otherwise you'll be able to create a perpetum mobile by using this membrane to filter out pure water and then using pure water to dilute brine (it produces energy) on the other side of the membrane.

I did design a perpetual motion machine involving a really deep tube in the ocean with a RO membrane at the bottom, exploiting the slight density difference between fresh and salt water to produce the required pressure. I know it can't work, because if it did it would be producing energy from nothing, but I still can't figure out exactly why it wouldn't work.

I wonder if that's one of those things that really would work, but not because it's perpetual motion, but instead because it's taking energy out of the system that's already there. For instance, look at wind power: just stick up a windmill in a windy place and you get free energy. Except that's not quite free: there's energy in the atmosphere, which is causing this wind, so your windmill is removing (a very small amount of) energy from the atmosphere and converting it to electricity. It works ok because

That's not a forbidden class of perpetual motion machine. It ultimately gets it's energy from the sun. And you are quite limited in the amount of energy that you can extract that way. I've never designed one, but there are a few analogous systems that are (or were, before solar power got cheaper) operating on remote islands. They were all test systems and none of them was cost effective, but that's more a design and materials problem than anything basic.

The laws of physics are rather strict on this account: You must, absolutly must, have a pressure source or some form of energy input. You can get energy out when you dilute a solution, and must put energy in to seperate them. It is possible it'll be more efficient though, so you don't need as much pressu.re

You won't get water intoxication merely by drinking pure water. Regular drinking water contains such low proportions of minerals that, from a physiological perspective, drinking water is effectively pure water. The main problem with pure water is that it doesn't taste "right". If you've ever tried drinking distilled water... yuck.

At the very least, it could be used for agriculture. Plants don't exactly care how water tastes. It could probably be used in soft drinks as well. Plus making cooling water that doesn't corrode stuff or build up residue - I can imagine this being used in nuclear reactors.

If it really is as simple as "run water through graphene sheets, get 100% pure hydrogen oxide", there's no limit to how many places it could be used.

Water intoxication can happen with either tap water or ultrapure water.

If you add hydration you need to add electrolytes or your system goes out of balance. Your body can handle only so much imbalance. As it goes too far out of whack, that's effectively water intoxication.

Drinking a glass of ultrapure probably won't hurt you, nor a glass of tap. But have a bunch of either in a short period and you will have a problem. Read the Wikipedia water intoxication article's "

I understand that one of the current problems with desalination filtering is that the salt left behind clogs up the filter fairly quickly. Hopefully researchers will test to know for sure, but this may well suffer from the same problem. The other problem is that the water wants to be with the salt - ie. it's an energetically stable state. You have to put in some energy (usually via pressure) to get it through a filter and away from the salt. Compare that to simply filtering out fine particulates that might

If it's really only letting water through, you'd still have to add minerals in at the other end. Last I checked, drinking distilled pure water is probably as bad as drinking salt water.. With salt water your body accumulates too much salt. With distilled water. all the minerals (that your body needs to function) get picked up by the water. However it it works well, it would be simple to add minerals back in after everything had been extracted.

Spend a little time thinking about it, and you will realize that distilled water urban legend is silly. In your mouth, it is mixed with saliva and mucous and whatever else is stuck to your teeth, gums, and tongue. The instant it hits your stomach, it is mixed with stomach acids and whatever you ate recently. I.e. it is no longer pure distilled water. From there, the molecules wander through your body like any other water molecule. Distilling water does not give its component molecules magic properties.

The problem, I think, is if you only drink distilled water, the electrolytes and minerals that leave your system in urine aren't being replaced as fast as they are when you drink tap water. Sure, you'll get some from food, but much less than normal. This could be a major issue, especially if you are drinking a lot of water. I.e. drinking a lot of distilled water could result in electrolyte depletion that would not happen with tap water. But this is probably something very few people will ever be in danger o

I'm a Ph.D. Chemist who has done some water purification studies. One difficulty is the build-up of particulate matter on/in the filter which slows down (eventually stops) flow through the filter.

This problem can be addressed with the use of two filters in parallel, one of which is being back-flushed while the other operates. With the current types of filters, the system eventually plugs due to micro particulates. Perhaps this Graphine filter is immune to plugging, and merely flushing the surface will cl

I imagine the water doesn't stay super-pure for long either, after it follows a Big Ma^H^H vegan soy burger that tastes like dust into your stomach where all the other food you ate in the last couple hours is.

Regular drinking water has such a small amount of dissolved minerals in it that, from a physiological perspective, it's effectively pure. If 10 gallons of tap water would give you water intoxication, then 9.99 gallons of pure distilled water would have the same effect. That's probably well within the error range of measuring the effect of the intoxication in the first place.

Informative? How about flamebait. This is simply not true. Absolutely insanely pure water is just water. Your body doesn't react to a 0.0001% difference in dissolved solids. After a microsecond in your mouth the water is far from pure.

Ah, making stuff up on Slashdot. Pure water might pull a little bit of salt from surrounding tissue. It's no big deal. It quickly becomes not-so-pure water. Any drinkable water is considerably purer than your bodily fluids and so there will be osmotic pressure.

I've drunk multi-distilled water and it's fine. I grew up drinking ordinary distilled water because our town water was so hard, and it's fine. Except for tasting slightly different, there's no noticeable effect.

He's not spreading FUD. Pure H2O is possibly the most corrosive chemical in the universe and IS certainly the most corrosive chemical in the known universe. The second the stuff hits your mouth it'll leech all the minerals from your teeth. God only know what it would do to the soft tissues, but you can be certain the sodium will be gone and the cell membranes will collapse due to the saline imbalance. Nerves would certainly be rendered useless in the vicinity of the water contact as well. It would lite

if you only drink pure water, and you only use pure water for cooking (with otherwise normal ingredients for a reasonably healthy diet), you will be perfectly fine.if you're talking about a specific scenario (i.e. running a marathon or something similar), I would have to ask a doctor, but you should also mention this in your post.

People don't get any significant amount of electrolytes from drinking water. So it doesn't matter the situation. Any potable water, fresh, distilled or ultra distilled, it's all the same as far as your body is concerned.

Not literally every water mollecule. There's A LOT of chemical reactions that produce water as a product or byproduct. If I remember my chemistry classes correctly, these water molecules were possibly created.

Hm... When hydrogens separate from oxygens, do they always take their original electron back? Or are we getting a random one out of the, say, two valence electrons the molecule was using previously? If we're possibly getting a different electron, isn't there a constant swap going on in the universe, for perhaps all covalent molecular configuration changes?

That is, atoms reform constantly?

So, the hydrogen and oxygen atoms that make up water could themselves be relatively fresh.

What about the Water Memory [wikipedia.org]? Does this membrane erase all this information or is a there a mechanism to determine which information to be deleted? Would be an invaluable Material for all that homeopathy stuff...

Seems a bit weird to respond to a scientific discussion, with scientific proof and evidence, with an article that says "No scientific evidence supports this claim".
It's equivalent to sitting in an evolution debate and proposing the idea of creationism.:-p

What about the Water Memory [wikipedia.org]? Does this membrane erase all this information or is a there a mechanism to determine which information to be deleted? Would be an invaluable Material for all that homeopathy stuff...

Water has no memory. You are being lied to so people can make money off you.If you want cheap homeopathic results just drink tap water and believe it is fixing you.With the proper belief you will get the benefit of the placebo effect without paying extra and as a bonus you can believe that the water is doing a whole host of killer things for you.

If this process were used in bootlegging, it would eliminate the still's heat signature. It would eliminate the still's distinctive sound. It might make it economical for many people to have their home stills in their garages. I see governmental regulation soon.

There are a variety of organic molecules that can be produced by fermentation (ethanol, butanol, etc) suitable for use as liquid fuels, that would be enormously more practical if the distillation process could be made more efficient. When the goal is water removal, this type of filter should be able to make industrial-scale vacuum distillation much simpler.